The overall purpose of this grant is to understand the phenotypic effect of mutations that cause hemochromatosis and to identify genetic polymorphisms that may modify the phenotype. More than 41,000 DNA samples are available from consenting patients who attended the Kaiser Permanente Health Appraisal Clinic and extensive health data including serum ferritin and transferrin saturation and HFE genotype have been obtained on virtually all of these subjects. Data collection will be continued on all of the patients who continue to receive their care in the Kaiser Permanente system and longitudinal studies will be conducted on this patient cohort, particularly with respect to the effect of the C282Y and H63D polymorphisms on the incidence of cardiovascular disease and of cancer. The candidate gene approach will be used to identify genes that may play a role in iron homeostasis. When polymorphisms are identified in such genes it will be determined whether they influence the phenotype of homozygotes for the C282Y mutation and whether they have any effect on serum transferrin saturation and ferritin levels. Promising candidates to be studied include haptoglobin and Nramp1. Attempts will be made to identify new candidate genes. These include the juvenile hemochromatosis (JH) gene located on chromosome lq and the putative hepcidin receptor. The region to which the JH has been localized positionally from other families is not accurately represented in GenBank, and its structure will be established. Then a comparison will be made of the sequence of genes within this interval from members of a family with lq linked juvenile hemochromatosis and controls. Since no genes known to be involved in iron metabolism are present in this interval, this should permit identification of a previously unknown modulator of iron homeostasis. Such a modulator might be involved not only in juvenile hemochromatosis but, presumably in the milder or heterozygous form, in modifying the phenotype of HFE hemochromatosis. The hepcidin receptor will be isolated by making antibody against hepcidin, binding hepcidin to cells, cross-linking and precipitating with antibody. Alternatively, isolation will be achieved by transfecting a cell line that does not bind hepcidin with a cDNA library made from cells that do express the receptor. The projected studies should improve our understanding of control of iron metabolism and make possible detection of those cases of hemochromatosis who are likely to become clinically affected.